As printing technology advances, paper manufacturers (or manufacturers of other printable substrates) are faced with the increasingly rigorous demands of their customers for high quality printable substrates that are economically attractive. For example, there is a great demand for printable substrates having an opaque or semi-opaque outer layer on their surface that can be rendered clear or semi-opaque to produce a printed medium that is useful in advertising and/or for producing attractive labels on products. Particularly needed are printable substrates with high enough quality to be suitable for printing of a digital image with an ink-jet printer, wherein the outer layer of the substrate is capable of being rendered either semi-opaque or clear is constructed upon a clear, semi-opaque, colored, or a reflective substrate layer (such as a metallic looking reflective substrate layer).
There is a keen demand for substrates that meet high quality standards with respect to brightness, opacity, and dry and/or wet strength, and that, upon printing with any of a wide range of colorants, provide a water-resistant printed image. The ability of such substrates to yield a printed substrate having high resolution and clarity without bleeding or mottling of the image, even when using ink jet printing has become in very high demand. Also, such substrates need to have appropriately smooth or textured surfaces that can be easily received by a non-impact printing system and to avoid curling surfaces that can clog printing equipment. Customers further demand that such substrates be amenable to use with a variety of printing techniques, including not only conventional printing techniques, but also “impact free” printing techniques such as inkjet printing (particularly colored inkjet printing), laser printing, photocopying, and the like.
In one market area such substrates are particularly desired that have the ability to produce a metallic-looking image on the substrate, and perhaps even a holographic image. In another market area, there is needed clear base substrates with a printed image that can be used with a projector for presentations. Also, clear base substrates having an adhesive backing for applying to articles of commerce are particularly in demand. A particularly high demand is for holographic labeling, since this is very difficult and expensive to produce and can be in high demand if an appropriate quality label can be produced.
Published U.S. patent application Ser. No. 2001/0051217 A1 (hereinafter 51217 application) relates to a process for producing a light-emitting, glossy, reflective or metallic-looking image utilizing opaque coating compositions on a reflective, glossy, or luminescent substrate wherein the original surface of the substrate is initially masked but, after contact with a recording liquid, becomes transparent, revealing the glossy, reflective or luminescent substrate through the contacted, coated area. The opaque coating compositions are composed of a mixture of a polyacid and a polybase and may be used to treat a substrate either during or after manufacture. Substrates treated with the present opaque coating compositions can be used to yield high quality light-emitting, glossy, reflective, or metallic-looking images.
However, the process, compositions and substrates described in the 51217 application suffered from a number of serious drawbacks and disadvantages that made their manufacturing and use not so desirable. The single layer composition of the substrate (or multiple coats of the single composition) and the make-up of the composition created a slow drying time after application of the image to substrate. The surface of the substrate (that was manufactured and printed as described in the 51217 application) can remain tacky for ten minutes up to several hours, which means that printing multiple copies, or multiple pages, can cause the tacky pages to adhere together and mar the printed substrate. A commercially viable product needs to dry from immediately up to a very few minutes. In addition, the 51217 substrate could allow bleeding on several types of the most commonly used printers or dispersion of the printed image that led to poor resolution in printed images. Also, when the layer was thick enough to avoid bleeding, it would sometime not become adequately transparent upon printing of an image.
There is a need for improving substrates have an initially opaque coating (or similar coatings) such as those described in the 51217 application in order, but without the drawbacks and disadvantages described above, in order to provide a printed substrate having an improved resolution and clarity without bleeding or mottling of the image, even when using ink jet printing device. There is a need to have printable substrates that have improved drying times to avoid excessively tacky surfaces and undesired adhering of multiple sheets. Also, there is a need to provide improved substrates from many different types of starting substrates (base substrates) having an initial base coating that will adhere well to a variety of such substrates and yet still accept coatings of the initially opaque (or semi-opaque) layers similar to those described in the 51217. There is a need to thereby provide light-emitting, reflective, glossy, metallic-looking or holographic images on a wide variety of substrate types and products, particularly as rolls, cut sheets, and labels for articles of commerce.
Accordingly, there is a need in the art for a simple and inexpensive process for the printing of light-emitting, reflective or metallic-looking glossy, metallic-looking or holographic images on a wide variety of substrate types and products, which have acceptable drying times and improved image clarity.